1. Field of the Invention
This invention relates to an apparatus for measuring the refraction of eye (eye refractometer) for use in ophthalmic hospitals, opticians or the like.
2. Related Background Art
A conventional refractometer of the type to which the present invention is pertinent is disclosed, for example, in the specification of U.S. Ser. No. 755,362 of the present application. The refractometer is provided with a projection optical system for projecting an index mark onto the eye fundus of an eye to be examined through a first aperture stop disposed substantially conjugate with the pupil of the eye, and a measuring optical system for guiding, to light-position detecting means, the light beam of the index mark reflected from the eye fundus through a second aperture stop disposed substantially conjugate with the pupil of the eye. The first and second aperture stops have each three spot openings arranged on an arc and extending in three meridian directions. The positions of the three spot openings are determined so when they are projected on the pupil of the eye to be examined, the respective images of the spot openings will be symmetric to the optical axis in the three meridian directions.
However, it has been found that the above-mentioned type of refractometer is unsatisfactory in the following points: the apparatus cannot give information of eye refraction other than that in three meridian directions; measurement errors tend to be caused especially when the measured eye is of irregular astigmatism; extremely high precision is required in setting the light-position detector means in the three meridian directions.